node.js is not an architecture, is a "software platform" for running a "language" (javascript) server-side.
An examples of a computer architectures are x86, amd64, MIPS, ARM, SPARC, POWER.
"For example, at a high level, computer architecture may be concerned with how the central processing unit (CPU) acts and how it uses computer memory." [http://en.wikipedia.org/wiki/Computer_architecture]
Now there also is a software architecture which is the abstract design of a system: "The word software architecture intuitively denotes the high level structures of a software system. It can be defined as the set of structures needed to reason about the software system, which comprise the software elements, the relations between them, and the properties of both elements and relations" [http://en.wikipedia.org/wiki/Software_architecture]
But node.js is neither of these.
Which will lead to what looks like fragmentation, but really isn't.